Wheel-driven heavy machinery, such as articulated trucks and graders/scrapers, operate under a wide variety of conditions that require different amounts of driving force (i.e., torque) to be produced by an output of a drive train to propel the machinery. Such conditions include surface types, grades, and cargo payload conditions. Moreover, a vehicle drive train control takes into consideration the expectations of a human operator, as indicated for example by a current throttle position. Thus, at least one important aspect of the vehicle drive train control is to take into consideration current operating conditions and driver demand and render responsive vehicle drive train control commands (e.g., increase fuel/air flow, reduce/increase transmission gear ratio, etc.).
A transmission gear/shift selection control method is described in Kresse U.S. Pat. No. 7,499,784. A shift schedule is selected for a transmission on an open-road (e.g., semi-trailer) truck based upon sensed conditions. In particular, the shift schedule is selected based upon a vehicle mass and an estimated road grade. In the example, a road grade estimate is calculated based upon a current vehicle mass (including payload) and tractive effort by the drive train. The net force causing acceleration of a truck is determined by subtracting a variety of forces (braking, drag, and grade) from the torque generated by the drive train upon the wheels. A recursive least squares estimator with forgetting facilitates generating a first estimate of road grade from the aforementioned parameter values. A second grade estimate provides an alternative grade value when poor signal-to-noise ratio conditions are detected. The vehicle mass estimate and a grade estimate, provided by one of the two alternative grade estimate sources, provide inputs to a transmission control that switches between performance (high power) and economy (high mileage) modes.
Nitz EP App. Pub. No. 0 512 596 A1 describes a shift pattern control in which upshifting/downshifting is modified in response to changes in road load. Above normal road load conditions can occur when a vehicle is towing a trailer, traveling a steep grade, and/or when unusual aerodynamic loading is encountered. When excessive road load is detected a shift pattern is adopted characterized by earlier downshifting during deceleration and later upshifting during acceleration of a vehicle traveling under above normal road load conditions.
Shortcomings in the state of the art are addressed by aspects of an exemplary method and transmission assembly (including a controller thereof) described herein.